Does the mouse C4-binding protein gene (C4BP) map in the H-2 region?

A previous study on the genetics of mouse C4-binding protein (C4-bp) indicated the existence of a genetic polymorphism. Two genetic variants were reported and their segregation used to determine the mapping position of the C4BP locus to the H-2D-Qa interval of the mouse H-2 system. We show here, however, that purified C4-bp does not display the previously reported polymorphism. The mapping position of C4BP in the mouse therefore remains undetermined.     

Ecotypic differences in the C3 and C4 photosynthetic activity in Mollugo verticillata,a C3−C4 intermediate

Four populations of Mollugo verticillata L. were compared on the basis of their photosynthetic products, photosynthetic rates, enhancement under low oxygen concentration, and CO₂ compensation points. In addition, pulse-chase labeling experiments were conducted using one of the four populations. Depending on the plant population, C₄ acids ranged from 40% to 11% of the primary products under short-term exposure to ¹⁴CO₂. These compounds were also metabolized during pulse-chase experiments. All four populations had significantly different photosynthetic rates and those rates were correlated with the amounts of labelled C₄ acids produced and C₄-acid turnover. Three populations of M. verticillata had similar compensation points (40 l/l) and degrees of photosynthetic enhancement under low [O₂] (20%), the fourth population was much lower in both characteristics (CO₂ compensation, 25 l/l; low-O₂ enhancement, 12%). The results verify the intermediate nature of photosynthesis in this species, and illustrate populational differences in its photosynthetic and photorespiratory carbon metabolism.Abbreviations PGA 3-phosphoglyceric acid - Kan Kansas - Mass Massachusetts - Mex Mexico     

Quo vadis C4? An ecophysiological perspective on global change and the future of C4 plants

C₄ plants are directly affected by all major global change parameters, often in a manner that is distinct from that of C₃ plants. Rising CO₂ generally stimulates C₃ photosynthesis more than C₄, but C₄ species still exhibit positive responses, particularly at elevated temperature and arid conditions where they are currently common. Acclimation of photosynthesis to high CO₂ occurs in both C₃ and C₄ plants, most notably in nutrient-limited situations. High CO₂ aggravates nitrogen limitations and in doing so may favor C₄ species, which have greater photosynthetic nitrogen use efficiency. C₄ photosynthesis is favored by high temperature, but global warming will not necessarily favor C₄ over C₃ plants because the timing of warming could be more critical than the warming itself. C₃ species will likely be favored where harsh winter climates are moderated, particularly where hot summers also become drier and less favorable to C₄ plant growth. Eutrophication of soils by nitrogen deposition generally favors C₃ species by offsetting the superior nitrogen use efficiency of C₄ species; this should allow C₃ species to expand at the expense of C₄ plants. Land-use change and biotic invasions are also important global change factors that affect the future of C₄ plants. Human exploitation of forested landscapes favors C₄ species at low latitude by removing woody competitors and opening gaps in which C₄ grasses can establish. Invasive C₄ grasses are causing widespread forest loss in Asia, the Americas and Oceania by accelerating fire cycles and reducing soil nutrient status. Once established, weedy C₄ grasses can prevent woodland establishment, and thus arrest ecological succession. In sum, in the future, certain C₄ plants will prosper at the expense of C₃ species, and should be able to adjust to the changes the future brings. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interspecific variation in assimilation of 14CO2 into C4 acids by leaves of C3, C4 and C3−C4 intermediate Flaveria species near the CO2 compensation concentration

The assimilation of ¹⁴CO₂ into the C₄ acids malate and aspartate by leaves of C₃, C₄ and C₃–C₄ intermediate Flaveria species was investigated near the CO₂ compensation concentration ^* in order to determine the potential role of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) in reducing photorespiration in the intermediates. Relative to air concentrations of CO₂, the proportion of CO₂ fixed by PEP carboxylase at ^* increased in all six C₃–C₄ intermediate species examined. However, F. floridana J.R. Johnston and F. ramosissima Klatt were shown to be markedly less responsive to reduced external CO₂, with only about a 1.6-fold enhancement of CO₂ assimilation by PEP carboxylase, as compared to a 3.0- to 3.7-fold increase for the other C₃–C₄ species examined, namely, F. linearis Lag., F. anomala B.L. Robinson, F. chloraefolia A. Gray and F. pubescens Rydb. The C₃ species F. pringlei Gandoger and F. cronquistii A.M. Powell exhibited a 1.5- and 2.9-fold increase in labeled malate and aspartate, respectively, at ^*. Assimilation of CO₂ by PEP carboxylase in the C₄ species F. trinervia (Spreng.) C. Mohr, F. australasica Hook., and the C₄-like species F. brownii A.M. Powell was relatively insensitive to subatmospheric levels of CO₂. The interspecific variation among the intermediate Flaverias may signify that F. floridana and F. ramosissima possess a more C₄-like compartmentation of PEP carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) between the mesophyll and bundle-sheath cells. Chasing recently labeled malate and aspartate with ¹²CO₂ for 5 min at ^* resulted in an apparent turnover of 25% and 30% of the radiocarbon in these C₄ acids for F. ramosissima and F. floridana, respectively. No substantial turnover was detected for F. linearis, F. anomala, F. chloraefolia or F. pubescens. With the exception of F. floridana and F. ramosissima, it is unlikely that enhanced CO₂ fixation by PEP carboxylase at the CO₂ compensation concentration is a major mechanism for reducing photorespiration in the intermediate Flaveria species. Moreover, these findings support previous related ¹⁴CO₂-labeling studies at air-levels of CO₂ which indicated that F. floridana and F. ramosissima were more C₄-like intermediate species. This is further substantiated by the demonstration that F. floridana PEP carboxylase, like the enzyme in C₄ plants, undergoes a substantial activation (2.2-fold) upon illuminating dark-adapted green leaves. In contrast, light activation was not observed for the enzyme in F. linearis or F. chloraefolia.Abbreviations and symbols PEP phosphoenolpyruvate - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - CO₂ compensation concentration - ^* a subatmospheric level of CO₂ approximating Published as Paper No. 8832, Journal Series, Nebraska Agricultural Research Division     

Increasing the stability of immobilizedLactococcus lactis cultures stored at 4 °C

Summary Immobilized cell technology was used to prepare concentrated cultures ofLactococcus lactis that lost only 22% of viability over a 30-day storage period at 4°C. Concentrated cultures ofL lactis CRA-1 were immobilized in calcium alginate beads and added to glycerol, NaCl or sucrose-NaCl solutions in order to obtain a_w readings ranging from 0.91 to 0.97. The suspensions were subsequently placed at 4°C and viability (CFU g^–1 of bead) was followed during storage. Viability losses were high at a_w readings of 0.95 and 0.97 and pH dropped significantly (up to one unit) in the unbuffered solutions. Addition of 1% soytone or glycerophosphate helphed stabilize pH, and a beneficial effect on viability during storage was observed in the glycerol-soytone mix when the beads were added to the conservation solutions immediately following immobilization. When beads were added to the conservation solution immediately following immobilization, a 70% drop in cell counts occurred during the first 5 days of incubation. Dipping theL lactis-carrying beads in milk for 2h before mixing with the glycerolsoytone 0.93 a_w solution reduced this initial 5-day viability loss. Cultures grown in the alginate beads also had good stability in the 0.93 a_w glycerol-soytone solution, where 78% of the population was viable after 30 days at 4°C. The process could be used to store immobilized cells at a processing plant, or by suppliers of lactic starters who wish to ship cultures without freezing or drying.     

Evolution of the C(4) photosynthetic mechanism: are there really three C(4) acid decarboxylation types?

Some of the most productive plants on the planet use a variant of photosynthesis known as the C(4) pathway. This photosynthetic mechanism uses a biochemical pump to concentrate CO(2) to levels up to 10-fold atmospheric in specialized cells of the leaf where Rubisco, the primary enzyme of C(3) photosynthesis, is located. The basic biochemical pathways underlying this process, discovered more than 40 years ago, have been extensively studied and, based on these pathways, C(4) plants have been subdivided into two broad groups according to the species of C(4) acid produced in the mesophyll cells and into three groups according to the enzyme used to decarboxylate C(4) acids in the bundle sheath to release CO(2). Recent molecular, biochemical, and physiological data indicate that these three decarboxylation types may not be rigidly genetically determined, that the possibility of flexibility between the pathways exists and that this may potentially be both developmentally and environmentally controlled. This evidence is synthesized here and the implications for C(4) engineering discussed.     

C3、C4和C3-C4中间型植物的进化

介绍了有关C3、C4和C3-C4中间型植物进化的形态学、生理学、分子生物学、遗传学等方面的证据;推断地球上首先出现C3植物,然后是C3-C4中间类型植物,最后出现C4植物.     

Effects of low atmospheric CO2 and elevated temperature during growth on the gas exchange responses of C3, C3–C4 intermediate, and C4 species from three evolutionary lineages of C4 photosynthesis

This study evaluates acclimation of photosynthesis and stomatal conductance in three evolutionary lineages of C(3), C(3)-C(4) intermediate, and C(4) species grown in the low CO(2) and hot conditions proposed to favo r the evolution of C(4) photosynthesis. Closely related C(3), C(3)-C(4), and C(4) species in the genera Flaveria, Heliotropium, and Alternanthera were grown near 380 and 180 μmol CO(2) mol(-1) air and day/night temperatures of 37/29°C. Growth CO(2) had no effect on photosynthetic capacity or nitrogen allocation to Rubisco and electron transport in any of the species. There was also no effect of growth CO(2) on photosynthetic and stomatal responses to intercellular CO(2) concentration. These results demonstrate little ability to acclimate to low CO(2) growth conditions in closely related C(3) and C(3)-C(4) species, indicating that, during past episodes of low CO(2), individual C(3) plants had little ability to adjust their photosynthetic physiology to compensate for carbon starvation. This deficiency could have favored selection for more efficient modes of carbon assimilation, such as C(3)-C(4) intermediacy. The C(3)-C(4) species had approximately 50% greater rates of net CO(2) assimilation than the C(3) species when measured at the growth conditions of 180 μmol mol(-1) and 37°C, demonstrating the superiority of the C(3)-C(4) pathway in low atmospheric CO(2) and hot climates of recent geological time.     

δ13C values of an herbivore and the ratio of C3 to C4 plant carbon in its diet

Summary The ¹³C values of whole body samples of the beetle Tribolium castaneum are closely correlated with the ¹³C values of the plant carbon in its diet. The correlation is always high for diets ranging from 100% C₄ to 100% C₃ plant material. The degree of correlation is independent of the growth rate of the animals.     

Transition from C3 to proto-Kranz to C3–C4 intermediate type in the genus Chenopodium (Chenopodiaceae)

The Chenopodiaceae is one of the families including C₄ species among eudicots. In this family, the genus Chenopodium is considered to include only C₃ species. However, we report here a transition from C₃ photosynthesis to proto-Kranz to C₃–C₄ intermediate type in Chenopodium. We investigated leaf anatomical and photosynthetic traits of 15 species, of which 8 species showed non-Kranz anatomy and a CO₂ compensation point (Γ) typical of C₃ plants. However, 5 species showed proto-Kranz anatomy and a C₃-like Γ, whereas C. strictum showed leaf anatomy and a Γ typical of C₃–C₄ intermediates. Chenopodium album accessions examined included both proto-Kranz and C₃–C₄ intermediate types, depending on locality. Glycine decarboxylase, a key photorespiratory enzyme that is involved in the decarboxylation of glycine, was located predominantly in the mesophyll (M) cells of C₃ species, in both M and bundle-sheath (BS) cells in proto-Kranz species, and exclusively in BS cells in C₃–C₄ intermediate species. The M/BS tissue area ratio, number of chloroplasts and mitochondria per BS cell, distribution of these organelles to the centripetal region of BS cells, the degree of inner positioning (vacuolar side of chloroplasts) of mitochondria in M cells, and the size of BS mitochondria also changed with the change in glycine decarboxylase localization. All Chenopodium species examined were C₃-like regarding activities and amounts of C₃ and C₄ photosynthetic enzymes and δ¹³C values, suggesting that these species perform photosynthesis without contribution of the C₄ cycle. This study demonstrates that Chenopodium is not a C₃ genus and is valuable for studying evolution of C₃–C₄ intermediates.

     

Semaphorin 4D Signaling Requires the Recruitment of Phospholipase Cγ into the Plexin-B1 Receptor Complex

The semaphorin 4D (Sema4D) receptor plexin-B1 constitutively interacts with particular Rho guanine nucleotide exchange factors (RhoGEFs) and thereby mediates Sema4D-induced RhoA activation, a process which involves the tyrosine phosphorylation of plexin-B1 by ErbB-2. It is, however, unknown how plexin-B1 phosphorylation regulates RhoGEF activity. We show here that activation of plexin-B1 by Sema4D and its subsequent tyrosine phosphorylation creates docking sites for the SH2 domains of phospholipase Cγ (PLCγ). PLCγ is thereby recruited into the plexin-B1 receptor complex and via its SH3 domain activates the Rho guanine nucleotide exchange factor PDZ-RhoGEF. PLCγ-dependent RhoGEF activation is independent of its lipase activity. The recruitment of PLCγ has no effect on the R-Ras GTPase-activating protein activity of plexin-B1 but is required for Sema4D-induced axonal growth cone collapse as well as for the promigratory effects of Sema4D on cancer cells. These data demonstrate a novel nonenzymatic function of PLCγ as an important mechanism of plexin-mediated signaling which links tyrosine phosphorylation of plexin-B1 to the regulation of a RhoGEF protein and downstream cellular processes.Mammalian semaphorins were originally identified as axon guidance factors but are now recognized also as important regulators of morphogenesis and homeostasis in various organ systems, including the immune, cardiovascular, and renal systems (3-5, 7, 19, 23, 30, 35, 40, 56, 64, 76). Most effects of semaphorins are mediated by a group of large transmembrane proteins called plexins, of which four families exist in the mammalian system: plexin-A1 to -4, plexin-B1 to -3, plexin-C1, and plexin-D1 (60, 61). The four members of the plexin-A family in most cases require neuropilins as ligand binding partners to respond to semaphorins, whereas the three members of the plexin-B family are directly activated by semaphorins. While plexin-B1 binds Sema4D, plexin-B2 can be activated by Sema4C and Sema4D, and plexin-B3 has been shown to respond to Sema5A (31, 35).The activation of plexins by semaphorins initiates a variety of signaling processes, which involve several small GTPases of the Ras and Rho families (31, 34, 43). All plexin family members possess an R-Ras GTPase-activating protein (GAP) domain (36). Activated plexin-B1 and -A1 have been shown to also interact with other small GTPases, including GTP-bound Rac1 and RhoD as well as Rnd1, Rnd2, and Rnd3 (14, 37, 48, 63, 67, 68, 74). Different from other plexin families, the C terminus of B-family plexins contains a PDZ domain-binding motif which mediates a stable interaction with the guanine nucleotide exchange factors PDZ-RhoGEF and LARG (1, 15, 26, 39, 57). Activation of the plexin-B1/PDZ-RhoGEF complex by semaphorin 4D (Sema4D) results in RhoA activation downstream of plexin-B1 (15, 39, 57). Members of the plexin-B family also interact with and are phosphorylated by the receptor tyrosine kinases ErbB-2 and c-Met (12, 22, 58). ErbB-2-mediated phosphorylation of plexin-B1 is required for plexin-mediated RhoA activation and downstream cellular effects, including the promigratory effects of Sema4D on cancer cells and the induction of axonal growth cone collapse by Sema4D (58, 59). However, the molecular mechanisms linking ErbB-2-mediated phosphorylation of plexin-B1 to the regulation of RhoA activity and subsequent cellular effects are unknown.Here we report that upon activation by Sema4D, plexin-B1 becomes phosphorylated by ErbB-2 at particular tyrosine residues on its intracellular portion. These phosphorylated tyrosine residues serve as docking sites for the SH2 domains of PLCγ. PLCγ is thereby recruited into the plexin-B1 receptor complex and through its SH3 domain mediates RhoA activation and downstream cellular effects.     

Production of somatic hybrids between Brassica oleracea and the C3–C4 intermediate species Moricandia nitens

Protoplast fusion between Brassica oleracea and Moricandia nitens, a C₃–C₄ intermediate wild species, was carried out. Four hundred and twenty five plants were regenerated from 1995 calli. More than 90% of the regenerated plants were verified as true intergeneric hybrids on the basis of morphological observation and molecular-marker analysis. The hybrids were morphologically intermediate between both fusion parents. Variations in flower color and petal number were also observed. The chromosome number and pollen fertility varied across the individual hybrids. Although after self-pollination pollen germinated on the stigma and pollen tubes were visible in the style, the pods did not develop properly without in vitro culture. Measurements of the CO₂ compensation point revealed that six out of eight hybrid plants expressed a gas-exchange character that was intermediate between the C₃–C₄ M. nitens and C₃ B. oleracea parents. Received: 20 January 1999 / Accepted: 16 June 1999     

Glycine decarboxylase is confined to the bundle-sheath cells of leaves of C3−C4 intermediate species

Immunogold labelling has been used to determine the cellular distribution of glycine decarboxylase in leaves of C₃, C₃–C₄ intermediate and C₄ species in the genera Moricandia, Panicum, Flaveria and Mollugo. In the C₃ species Moricandia foleyi and Panicum laxum, glycine decarboxylase was present in the mitochondria of both mesophyll and bundle-sheath cells. However, in all the C₃–C₄ intermediate (M. arvensis var. garamatum, M. nitens, M. sinaica, M. spinosa, M. suffruticosa, P. milioides, Flaveria floridana, F. linearis, Mollugo verticillata) and C₄ (P. prionitis, F. trinervia) species studied glycine decarboxylase was present in the mitochondria of only the bundle-sheath cells. The bundle-sheath cells of all the C₃–C₄ intermediate species have on their centripetal faces numerous mitochondria which are larger in profile area than those in mesophyll cells and are in close association with chloroplasts and peroxisomes. Confinement of glycine decarboxylase to the bundle-sheath cells is likely to improve the potential for recapture of photorespired CO₂ via the Calvin cycle and could account for the low rate of photorespiration in all C₃–C₄ intermediate species.Abbreviation and symbol kDa kilodaltons - CO₂ compensation point     

How is the relationship between the C4 cereal Sorghum bicolor and the C3 root hemi-parasites Striga hermonthica and Striga asiatica affected by elevated CO2?

The C₄ cereal Sorghum bicolor was grown under either ambient (350 μmol mol^?1) or elevated (700 μmol mol^?1) [CO₂] in either the presence or absence of the C₃ obligate root hemi-parasites Striga hermonthica or S. asiatica. Both uninfected and infected sorghum plants were taller and had greater biomass, photosynthetic rates, water-use efficiencies and leaf areas under elevated compared with ambient [CO₂]. There was no evidence of any downregula-tion of photosynthesis in sorghum grown at elevated [CO₂]. Biomass of infected sorghum was lower under both ambient and elevated [CO₂], and although infected plants were larger under elevated [CO₂] the relative impact of infection on host biomass was either the same (S. asiatica) or only slightly less (S. hermonthica) than under ambient [CO₂]. In contrast, biomass of S. hermonthica and S. asiatica per host was lower under elevated than ambient [CO₂], although rates of photosynthesis were higher at elevated [CO₂] and parasite stomatal conductance was not responsive to [CO₂]. Parasites emerged above-ground and flowered earlier under ambient compared with elevated [CO₂]. It appears that the mechanism(s) by which the parasites affect host growth is (are) relatively insensitive to increased atmospheric [CO₂], although the parasites themselves were adversely affected by growth at elevated [CO₂].     

C4植物的光呼吸

自50年代 Decker 发现光呼吸后的一段时间里,有些学者认为 C_4植物是非光呼吸型的。70年代以后,越来越多的人证明 C_4植物是有光呼吸的。本文报道我们近年来对 C_4植物光呼吸测定的结果。